This invention relates to recording members and more particularly to pressure-sensitive recording members, heat-sensitive recording members, electricity-sensitive recording members and light-sensitive recording members which are capable of providing color images having excellent light fastness.
Although a number of recording methods utilizing energy such as pressure, heat, light and electricity have heretofore been proposed, an extremely limited number of methods have been put in practical use. Generally in such recording methods using pressure-sensitive copying paper, heat-sensitive recording paper, or electricity-sensitive recording paper which are presently in practical use, the phenomenon utilized is that when an electron donor substance, dye precursor (which is also called "a color former", and which is a substantially colorless compound forming color on reacting with an electron acceptor substance) and an electron acceptor substance (which is also called "a developer" and an acidic substance, exemplified by clay minerals such as activated clay, phenols, organic carboxylic acids or the metal salts thereof) are brought in contact with each other with application of pressure, heat, and/or electricity, they undergo a chemical reaction and form colored substances.
As a light-sensitive recording sheet, a silver salt light-sensitive member and a diazo light-sensitive paper are well known. Light-sensitive recording sheets, however, of the type that the above-described dye precursor is used in combination with a compound which releases an electron acceptor substance by application of light have been proposed and disclosed, for example, in Japanese Patent Publication Nos. 24188/63, 10550/70, 13258/70, 6212/74, and 28449/74, and Japanese Patent Application (OPI) Nos. 80120/75 and 126228/75 (The term "OPI" as used herein refers to a "published unexamined Japanese patent application").
Dye precursors for use in recording members which form color on coming in contact with electron acceptor substances are required to meet with a number of requirements. Some of the major properties are as follows: (1) they are substantially colorless compounds, (2) they form deep color almost instantaneously on coming into contact with electron acceptor substances, (3) they are easily soluble in certain organic solvents, (4) they have no sublimation properties, (5) they are free from decomposition or coloring due to light, heat, moisture, etc., during the storage thereof, (6) formed color images are fast to light, heat, moisture, chemicals, etc., (7) they are not toxic and cause no environmental pollutions, and (8) they can commercially be produced at low costs.
However, no dye precursors forming blue or black color which meet with all the requirements have been known. Thus, color formers are presently used in admixtures comprising two or more thereof or in combination with suitable electron acceptor substances. For example, Crystal Violet Lactone, having the structure (A) as shown below, and which is presently in practical use as a blue color former, fails to satisfy property (6), although it does satisfy properties (2) and (5). It is, therefore, used in combination with N-Leucobenzoylmethylene Blue having the structure (B) as shown below which does satisfy property (6) although it does not satisfy properties (2) and (5). These methods, however, suffer from the disadvantages that Crystal Violet Lactone and N-Leucobenzoylmethylene Blue have different color formation hues, and when exposed to light before dye formation, become colored. ##STR1##
Fluoran based color formers having the structure (C) as shown below which can be practically used as red or black color formers, when used in combination with activated clay as an electron acceptor substance, provide color images which are high in color intensity, but low in light resistance. On the other hand, when a phenol resin is used as the electron acceptor substance, the color intensity is low although the light fastness is improved. ##STR2##
As described above, the conventional color formers have various disadvantages, and have constituted a major obstacle to improvements in the performance of image recording members such as pressure-sensitive copying paper, etc.